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Discussion Starter · #1 ·
I have a sony 1252 and last night after watching a movie I turned the projector off only to find that the green tube still had a faint glow to it. Both the red and blue faded away almost instantly but the Green continued to glow even up to 10 minutes later (I went to bed after that) I checked it this morning and all seems to be fine


I found it a bit odd that the blue and red faded straight away but the green lingered for so long. I even disconnected the power from the projector to see if this made a difference but it didn't.


So do I have a problem developing :( or is this normal ?????
 

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Normal ;) .

--- Jason
 

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It's entirely normal. The green phosphor tends to persist after shutdown. Do a search on "cold emission"


The following comments were made by Walter Allen of Elite Video:


"Regarding the inability to "cut off" the green tube, this is almost always due to a source of "cold emission", which is an always on, unwanted stream of electrons coming from some part of the electron gun. When present, this cold emission adds to the normal flow of electrons coming from the cathode, so even when the tube is truly cut off, you will seen a raster, although it will not be perfectly focused and there will be retrace lines since there it's always on. When you then turn up G2, you will see the normal raster appear in addition to the cold emission raster, but it will be focused and not exactly in the same place. You should use this focused raster to set the cutoff, while ignoring the cold emission. Note that even though the cold emission appears relatively bright while looking in through the lens, rarely is it bright enough to be seen on the screen, even with all colors cutoff."


Ray
 

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Discussion Starter · #4 ·
Thanks for the reply.


Good to known its nothing bad


I guess the next question is why?


Why does the green still glow but not the Blue or Red?
 

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One factor that causes this normal effect is that the green phosphors have a much longer decay time (persistance) than the other tubes. When the electron beam strikes the phosphor it produces light, however the light doesn't instantly turn off when the electron beam moves away. The light generated slowly tapers off.


For an interesting effect, set your screensaver to 'Starfield Simulation' and look into the different tubes. You will see long trails on the Green tubeface due to the long persistance.
 

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Ray,

I tried the search for cold emission but kept comming up with a picture of my mother in law...


Chip
 

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I also did a search on the subject of after glow. We can't talk about that here. Had nothing to do with CRT.


Chip
 

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Persistence is probably what you're seeing. Green phosphors are particularly susceptible to it.


Try this sometime: At night with the lights off, take a flashlight and shine it into the lenses of your projector when the projector is turned completely off.. Close your eyes while you do it so as not to lose your dark adaptation. Turn the flashlight off, and look at the tubes.


You'll see rather a lot of glow coming from the green tube, and maybe some from the red and blue tubes, too. Light can excite the phosphors, and they continue to emit light for a little while, just like phosphorescent paint.


That glow is not cold emission. That's something different.



CJ
 
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